Today's color television receivers provide reasonably acceptable picture quality provided that the signal to noise ratio is high. However, this level of receiver performance is achieved with partial frequency response both in the luminance and the chrominance channels. One usually considers the luminance frequency response as the dominating factor establishing picture resolution. We assume a line-comb filter, which removes some diagonal bandwidth and that the 483 active vertical lines provide effective resolution of 338 lines per picture height (Lines/PH) (i.e., a Kell factor of 0.7). Most of today's receivers provide effective horizontal bandwidth of 3.5 MHz (i.e., filter factor of 0.8 due to spot size and receiver/amplifier limitation), corresponding to effective horizontal resolution of 262 Lines/PH. The effective spatial resolution of today's NTSC is shown in FIG. 1.
Camera scanning of 525 lines can be replaced with a scanning rate of twice that or even 1125 lines with subsequent vertical filtering (or digonal filtering) and then subsampled to provide a compatible 525 line transmission signal. Overscanning in the camera has two positive effects: it reduces vertical aliasing and allows close to the full diagonal resolution of the system to be realized. If interfield filtering is used, reduction in line crawl and flicker can be achieved. While the latter improvement can be fully realized without receiver modification, the overscanning improvements would need corresponding receiver modifications to realize their full effect.
Vertical interpolation for display at the receiver can double the vertical line density at the display and thus provide the full advantages of the overscanning at the camera. A frame memory allows that with the advantage of scanning at 60 Hz non interlace. Frame comb filtering will eliminate artifacts such as cross color and cross luma. Temporal resolution loss due to frame comb filtering can be overcome by using adaptive filtering. See the discussion by G. Tong "Signal Processing for Higher Definition Television", IBA Technical Review, 21, p 13, (1983) and by M. Achiha, K. Ishikura and T. Fukinuki, "A Motion-Adaptive High Definition Converter for NTSC Color TV Signal", SMPTE J. 93, p 470, (1984). The technology for implementing the above receiver improvements exists today and new receivers employing frame memories and noninterlace interpolation displays are already being sold.
With the advent of these techniques, the NTSC format can be fully realized and thus Full NTSC provides full horizontal resoluton of 328 Lines/PH and a Kell factor of 0.9, yielding a vertical resolution of 435 Lines/PH, with a corresponding increase in diagonal resolution (see FIG. 1).